4. Intro to Vascular System

Introduction to Vascular System

  • Instructor: Dr. Declan McKernan

  • Email: declan.mckernan@universityofgalway.ie

  • Course: PM309 Cardiovascular Drugs

Learning Outcomes

  • Understand variability of blood pressure with location and cardiac cycle stages.

  • Identify regulation mechanisms of blood pressure, including systems and hormones involved.

Blood Pressure Mechanics

  • Dependence on two key valves:

    • Atrioventricular (AV) Valves

      • Open/close based on pressure differences between atria and ventricles.

      • Open when atrial pressure > ventricular pressure during relaxation.

    • Semilunar Valves

      • Open during systole when ventricular pressure exceeds arterial pressure.

      • Close during diastole to prevent reflux, ensuring unidirectional blood flow.

  • Cardiac Cycle Phases:

    • Systole:

      • Pressure rises in ventricles causing blood ejection.

    • Diastole:

      • Ventricles fill with blood as atria contract.

Cardiac Cycle Pressure Changes

  • Stages:

    • Isovolumic Relaxation: All valves closed, pressure decreases.

    • Atrial Systole: Atria contract, blood flows into ventricles.

    • Ventricular Systole: Ventricles contract, pumping blood into aorta and pulmonary artery.

Systemic Blood Pressure Regulation

Anatomy Overview

  • Major Structures:

    • Aorta, vena cava, pulmonary arteries and veins, hepatic and renal arteries and veins.

  • Blood Vessels Classification:

    • Elastic Arteries

    • Muscular Arteries

    • Arterioles and Capillaries

    • Venules and Veins

Blood Pressure Measurement

  • Technique: Auscultation using a sphygmomanometer.

  • Procedure: Inflate cuff on the brachial artery, measure

    • Systolic Pressure: First Korotkoff sound.

    • Diastolic Pressure: Last Korotkoff sound.

  • Normal Values:

    • Systolic: 120 mmHg, Diastolic: 80 mmHg, Mean arterial pressure: ~90 mmHg.

Regulation of Blood Pressure

  • Formula: BP = Cardiac Output (CO) x Total Peripheral Resistance.

  • Cardiac Output Calculation: CO = Heart Rate (HR) x Stroke Volume (SV).

  • Peripheral Resistance:

    • Depends on arteriole diameter.

    • Increased contraction leads to increased resistance.

Adrenergic Regulation

  • Role of norepinephrine and adrenergic receptors in regulating vascular smooth muscle responses.

  • Receptors:

    • Alpha-1: Causes contraction of vascular smooth muscle.

    • Beta-1: Increases heart rate and myocardial contractility.

    • Beta-2: Induces relaxation in smooth muscles.

Baroreceptor Reflex

  • Vagal nerves decrease heart rate via K+ channel opening.

  • Sympathetic system increases heart rate through norepinephrine secretion at β1 receptors.

  • Baroreceptors located in carotid sinus and aortic arch sense blood pressure changes.

Renin-Angiotensin-Aldosterone System (RAAS)

  • Renin Functions:

    • Enzyme released during volume depletion signals Na+/water retention, leading to vasoconstriction.

  • Steps of RAAS:

    • Renin cleaves angiotensinogen to angiotensin I, which converts to angiotensin II, causing vasoconstriction and aldosterone release.

Endocrine Regulation

  • Antidiuretic Hormone (ADH): Released from posterior pituitary; increases water retention and vasoconstriction.

  • Endothelium-derived mediators: Include nitric oxide (NO) and prostaglandins (PGs) that affect vascular smooth muscle tone.

Summary

  • Blood pressure is influenced by location, heart cycles, and is regulated systemically and locally by various factors, ensuring homeostasis.

robot